- Big Ideas
- Essential Questions
- Content Outcomes Addressed
- Standards Addressed
- Pre- and Post-Assessment
- Investigation 1: When Rain Reaches the Ground
- Extension: Where's the Scavenger Hunt?
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- When rain reaches the ground, it can infiltrate the surface or become runoff.
- Plant roots hold soil in place during rainfall so that erosion is limited.
- Human activities change the ground cover, varying the quality and quantity of runoff that reaches waterways.
- What determines how much rain becomes infiltrate and how much becomes runoff?
- What effect do plants have on water quality?
- How do changes in ground cover affect water quality?
Content Outcomes Addressed
- Students will understand how human activities that alter ground cover can lead to changes in water quality.
- Students will understand that rain can become infiltrate and/or runoff in varying percentages as a result of the characteristics of ground cover.
- Disciplinary Core Ideas: ESS2.A (K-5), ESS2.C (K-8), ESS3.A (K-2), ESS3.B (3-5), ESS3.C (K-8), LS2.C(6-8)
- Science and Engineering Practices: 1, 2, 4, 5, 6, 8
- Cross-cutting Concepts: 2, 3, 4, 6
- Writing: W.K.7, W.K.8, W.1.7, W.1.8, W.2.7, W.2.8, W.3.7, W.3.8, W.4.7, W.4.8
- Speaking and Listening: SL.K.1, SL.K.3, SL.K.5, SL.K.6, SL.1.1, SL.1.3, SL.1.5, SL.1.6, SL.2.1, SL.2.3, SL.2.6, SL.3.1, SL.3.3, SL.3.6, SL.4.1, SL.5.1, SL.6.1, SL.7.1, SL.8.1
- Measurement & Data: MD.B.3, 1.MD.C.4
National Geography Standards: 7, 14
Water is essential for life on Earth, but it can shape the nonliving environment as well. Human impact on ground cover can result in varying the quality and quantity of runoff and infiltration after rain and other precipitation events. When rain falls, a portion of the water soaks into the ground. This process is called infiltration. What does not infiltrate will flow over the ground and as runoff. Puddling or pooling occurs when rain cannot infiltrate, either due to soil saturation or impermeability, and stays in one spot on the ground. Puddles “disappear” as the water slowly infiltrates the ground as pore space becomes available or as the water evaporates into the atmosphere.
Humans can change ground cover through activities such as construction, paving, walking, farming, and grazing animals. For example, treading habitually on the ground can kill plant life and/or compact the soil so that runoff and pooling occur more frequently. An increase in runoff means a decrease in infiltration. Infiltrate is important for moisturizing the soil and providing water to plant roots. It also can recharge underground aquifers. As water moves through the soil, it is filtered and goes through chemical processes that further purify it. Also, eliminating plant life leads to erosion. More soil is lost in runoff, as there are no more roots to hold the soil in place. So runoff from bare soil that enters lakes and ponds carries sediment and impairs water quality of those water bodies.
infiltrate: precipitation that enters the soil
runoff: precipitation that flows over the ground rather than seeping into it
precipitation: rain, snow, hail, sleet, etc.
ground cover: soil, pavement, grass, concrete, etc.
erosion: the process by which water, ice, wind, and gravity reshapes the land by moving rocks, soil, and other weathered material
Pre- and Post-Assessment
- Assess prior knowledge by asking students to draw a picture of the water cycle. Have students repeat this activity after the unit of study.
- Describe a change that humans make to ground cover, such as cutting down a forest for farming, and ask the students what they predict will happen when it rains.
- All rain flows into puddles.
- Plants take up all the rain.
Investigation 1: When Rain Reaches the Ground
What happens to rain when it falls on the ground?
Materials (for each group of students)
- 1 tray with loose soil covering half of it
- 1 tray with compacted soil covering half of it
- 1 tray with soil planted with grass covering half of it
- Landscaping fabric/netting to separate the soil from the unfilled portion of each tray
- 3 spray bottles full of water
- Books to prop up each tray on an angle (soil section should be highest)
- Notebooks and pencils
(Experiment is modified from QUEST—Steve Carson, PhD, Princeton University.)
- Divide students into three groups and distribute materials detailed above.
- Tell each group to use books to prop its tray at an angle, with the soil section at the higher side.
- Each group should spray the soil in their angled trays with water in synchronized fashion.
- Instruct students in each group to keep track of the time it has been “raining” on their tray and at what time they start to see infiltrate/runoff from their soil into the empty portion of the tray, and record the data in their notebooks. Emphasize that these are the quantitative observations. Now ask the students to observe the quality (qualitative observations) of the runoff in each tray. Describe and compare the color and turbidity (i.e. transparency) of the infiltrate/runoff. Note any pooling/puddling on surface.
- As groups finish, ask the students to discuss with each other why they think the infiltrate/runoff from the grass tray is clearer (i.e. has less turbidity) than the infiltrate/runoff from either soil tray. Also discuss why there were puddles and when they formed.
Rain/Water is an important part of life. Without water plants would not grow and animals would either move to areas with water or die. Rain has many benefits, but can also cause erosion. Vegetation (because of the roots) helps soil to stay in place. Runoff from the grass tray is clearer because the grass roots are holding most of the soil in place so it does not wash away in the runoff. Pooling occurs mostly on the surface of the compacted soil because it takes longer for the rain to infiltrate the tightly packed soil. These puddles may slowly infiltrate the soil or be evaporated into the air. It is important for humans to recognize the effect construction projects and removing plants from ground cover can have on water quality.
Extension: Where's the Scavenger Hunt?
- To find evidence of water and water’s influence around us
- Scavenger card (list of things to look for). Examples: two things that store water, somewhere water goes, something water has changed, three different things that drink water,something that water helps grow. Make the list simpler for younger students; increase the number of each type of item on the list for older students.
- Using a scavenger list, ask students to find various effects of water. Upon returning, students can share their responses and be led in a discussion about the importance of water in shaping our environment.